In imaging apparatuses for diagnosis, that is, apparatuses which acquire images of a vascular lumen, there are, for example, an intravascular ultrasound (IVUS) apparatus and an optical coherence tomography (OCT) apparatus.
In the above-described imaging apparatus for diagnosis, an imaging core including a configuration of emitting ultrasound waves or light and a configuration of receiving reflected waves or light from a vascular tissue thereof is contained in a catheter sheath.
The OCT can obtain an image of a vascular lumen surface having high resolution. However, it is only possible to obtain an image from the vascular lumen surface to a relatively shallow tissue. Meanwhile, in a case of the IVUS, even though the resolution of an image, which can be obtained, is lower than that of the OCT, in contrast, an image of a vascular tissue deeper than that of the OCT can be obtained. Recently, an imaging apparatus for diagnosis having the function of the IVUS and the function of the OCT combined together (an imaging apparatus for diagnosis provided with an ultrasound wave transceiver which can transceive ultrasound waves and an optical transceiver which can transceive light) has been proposed (for example, refer to JP-A-11-56752 and JP-A-2006-204430).
Liquid which is a medium of transmitting signals transceived by an imaging core is sometimes contained in a space between the imaging core and a catheter sheath. For example, in a case of a diagnostic apparatus utilizing optical interference, the liquid is contained in the space between the imaging core and the catheter sheath, and thus, it is possible to facilitate the design of an optical member which is generally positioned at a distal end of the imaging core. The reason is that refraction of light can be reduced on an interface of the optical member and an interface of the catheter sheath by containing liquid having a refractive index closer to the refractive index of the optical member or the refractive index of the catheter sheath compared to the refractive index of air.
In addition, ultrasound waves are remarkably attenuated in the air, and when air is present between an ultrasound transducer and a test object, most of the ultrasound waves are totally reflected by the interface therebetween so that the ultrasound waves are not transmitted to the test object. In a case of IVUS, in order to minimize the attenuation or the total reflection of ultrasound waves caused by air so as to be as low as possible, a space between the imaging core and the catheter sheath can be filled with liquid, thereby suppressing degradation of propagation efficiency of ultrasound waves with respect to the test object.
In order to fill the space between the imaging core and the catheter sheath with liquid, air (air bubble) therebetween needs to be easily discharged to the outside. In other words, priming needs to be able to be easily performed. Therefore, generally, a hole for releasing air is provided in the distal end of the catheter sheath (side where the imaging core is present). The reason is that when liquid (generally, a physiological salt solution) is injected from the opposite end, air inside the catheter sheath can be discharged to the outside.
Incidentally, determining whether or not the priming is normally performed is based on the fact that liquid is discharged through the hole in the distal end of the catheter sheath, and the priming is considered to be completed. The reason is that the catheter sheath is an extremely small tube and it can be difficult to visually check the catheter sheath.
Moreover, on the contrary, the hole for releasing air provided in the distal end of the catheter sheath sometimes causes inconvenience. That is the problem of blood flowing into the catheter sheath through pull-back processing which can be performed after the distal end of the catheter sheath is positioned inside a blood vessel which is a diagnostic target. In the pull-back processing, since the imaging core is pulled along a rotary axis thereof while being rotated, the inside of the catheter sheath is under relatively negative pressure with respect to the outside of the catheter sheath. As a result thereof, blood flows into the catheter sheath through the hole in the distal end of the catheter sheath, thereby leading to a problem.
In addition, when a catheter indwells in a blood vessel for a long period of time, blood sometimes flows into the catheter sheath due to the blood pressure inside the blood vessel even though the pull-back processing is not performed. Since blood is an opaque liquid, in a case of the diagnostic apparatus utilizing optical interference, an obtained image is likely to be blurred.
Blood which has flowed into the catheter sheath can be removed by reinjecting liquid such as a saline, which is unlikely to influence a human body, through the proximal end of the catheter sheath similar to the priming. However, in order to realize the removal, there is a need to know that the blurred image is caused by blood flowing into the catheter sheath.